Azure APIM - Host Names and Base URLs

Hi,

I have 2 questions:

1. I have the architecture as Internet -> Azure App GW -> Azure API Manager. The host name exposed to internet is different , which basically is mentioned in APP Gateway, lets say: https://external_host and once the request reaches to APP GW, it forwards it to the Azure APIM host , lets say to : https://apim_host. Now the issue is for our customers when they login to the Azure APIM developer portal and look at the APIs then they see the URL and host name of the APIM which is https://apim_host. It will work fine if they test in developer portal , but that URL won't work for them if they integrate it with their system. For that they need to use the APP GW Host name which is https://external_host. How can I overwrite the host name in Developer Portal some how so that when customers login , they see the URL which they are supposed to integrate with ?
2. I also have Self Hosted GW enabled in Azure APIM. Now when I select that Gateway to the API, it shows the Base URL for the Managed ( External ) GW and not for the Self Hosted GW. How can we enable the host name for Self Hosted GW as the Base URL , so that it reflects that immediately while creating the API? Basically, there should be 2 Base URLs i.e. one for Managed GW and another for Self Hosted GW and it should toggle the Base URL depending on which GW the API will be deployed on.

Thanks.